The present invention relates to a diffractive optical element, an objective optical system including the same and an optical pickup including the same.
According to, for example, Patent Document 1 (Japanese Laid-Open Patent Publication No. 9-127321), in a diffractive optical element including a plurality of stacked optical parts (optical materials) and a relief pattern formed on at least one of boundary surfaces, the wavelength dependency of the diffraction efficiency attained on the boundary surface having the relief pattern is lowered by employing an architecture satisfying the following formulas:n1(λ)>n2(λ)[{n1(λ2)−n2(λ2)}/{n1(λ1)−n2(λ1)}]>[{n1(λ2)−1}/{n1(λ1)−1}]  (*)wherein λ1 and λ2 are arbitrary wavelengths and λ1<λ2, n1(λ) is a refractive index to light of a wavelength λ of one optical part facing the boundary surface, and n2(λ) is a refractive index to the light of the wavelength λ of the other optical part facing the boundary surface.